When an emergency call is made to an emergency center it is important to determine the location of the terminal from where the call was made. Authorities in many countries have therefore put positioning requirements on the telecommunication network operators. Traditional fixed line telephones are simply localized by their telephone numbers as these are affiliated with the physical address of the subscriber. For mobile terminals however other techniques are necessary. A method that has become a de facto standard in many countries is assisted GPS (A-GPS). A-GPS is based on traditional GPS positioning using GPS enabled mobile terminals. Although traditional GPS alone is a very precise positioning method it has its drawbacks in areas with poor GPS signal conditions as in buildings and dense urban areas. To improve the sensitivity and to speed up the time to fix the satellites in these situations A-GPS uses additional GPS data provided by the radio access network (RAN).
Another approach to positioning is called fingerprinting positioning, or RF fingerprinting. Fingerprinting positioning algorithms operate by creating a database of radio fingerprint data for each point of a fine coordinate grid that covers the RAN. The fingerprint data may include:                radio cell identities that are detected by the terminal, in each grid point        quantized signal strength measurements, with respect to multiple base stations, performed by a mobile terminal, in each grid point        radio connection information, such as the radio access bearer (RAB) etc.        
Whenever a position request for a particular mobile terminal is received, fingerprint data for the mobile terminal is first obtained. This fingerprint data is matched with the fingerprint database to retrieve the corresponding grid point and thus identify the location of the mobile terminal. Of course, this approach requires that the fingerprint data for each grid point is unique and that the fingerprint data obtained from mobile terminal at a given point is relatively consistent.
The database of fingerprinted positions (the radio map) can be generated in several ways. One approach is to perform an extensive surveying operation that performs fingerprinting radio measurements repeatedly for all coordinate grid points of the RAN. The disadvantages of this approach include that the surveying required becomes substantial, even for small RANs. Further, some of the radio fingerprint data (e.g. signal strength and path loss) is sensitive to the orientation of the mobile terminal. For fine grids, the accuracies of the fingerprinted positions therefore become highly uncertain. Unfortunately, these potential problems are seldom reflected in the accuracy estimates reported along with the reported geographical result.
Another approach to RF fingerprinting is to replace the fine grid by high-precision position measurements of opportunity, and to provide fingerprinting radio measurements for said points. This avoids a number of the above drawbacks.
Ericsson's Adaptive Enhanced Cell ID (AECID) is a fingerprinting method that collects for example A-GPS positioning data. The principle of the AECID method is for example described in the international patent application with the publication number WO2009/131506 and in the paper “AECID Fingerprinting Positioning Performance” by Liang Shi and Torbjörn Wigren published in the IEEE Globecom 2009 proceedings.
An AECID positioning server collects high precision position measurements of opportunity in positioning data records also called reference points, using for example A-GPS. The positioning data records are for example collected from serving or gateway mobile location centres, SMLC/GMLC and comprise determined geographical positions associated with radio network communication parameters that are recorded during the high precision positioning measurement.
For GSM, the associated radio network communication parameters comprise the CGI of a serving cell and of neighbour cells and the corresponding signal strengths. Corresponding communication parameters are recorded for other radio technologies.
All collected positioning data records can be saved in an intermediate storage for later processing.
The AECID fingerprinting method continues by grouping the high precision position measurements in clusters. The high precision position measurements of each cluster are tagged with the same set of serving cell and detected neighbour cells, as well as network measurements. For each cluster that has enough high precision position measurements, a geometrical shape representing a geographical area is computed.
A problem arises when the RAN is reconfigured and network configuration parameters (such as cell identities, radio systems types, antenna height etc) change. At these occasions a number of collected positioning data records become invalid or misleading. When such configuration parameter changes are made, existing positioning servers erase all the collected positioning data records related to the changed configuration parameters and a large number of positioning data records has to be collected anew in order to compute new valid geometrical shapes. This is turn also means that positioning data that still was valid becomes unavailable.